‫ە‬Research Trends and Results

Trial of riverine estuary environment
classification on first class rivers throughoutJapan


AMANO Kunihiko, HeadONUMA Katsuhiro, Senior Researcher
ENDO Maremi, Researcher
River Environment Division, Environment Department
Research Trends and Results(Key words) Riverine estuary, environment, classification 
1. Aims of the researchAt river mouths where rivers reach the ocean,riverine estuaries are formed by the mixing of fresh
water with salt water. In riverine estuaries, complex
physical and chemical phenomena occur as a result ofexternal forces including tides, waves, floods,
sediment supply, and addition of pollutants from boththe sea and from the river, and the combinations ofthese external forces produce diverse environmentalproperties. Living organisms adapted to thisenvironment inhabit these waters.
These complex and diverse riverine estuary
environments are often strongly impacted byman-made disruptions, so it is difficult to set goals
when planning the conservation of their environments.
If riverine estuaries can be classified according toenvironmental properties, it will be possible toevaluate the environmental impacts of specified
man-made changes by selecting and comparing rivers
with different degrees of man-made change fromamong multiple rivers in the same classification. And
if we select a river where relatively little man-madechange occurs as a reference, it might be possible toset environmental conservation goals for riverine
estuaries on rivers in the same class with considerable
objectivity. For these motivates, we classified riverine
estuaries on rivers nationwide by abstracting naturalenvironment elements presumed to determine theproperties of riverine estuary environments. 
2. Physical environment classification of riverine
estuaries on 109 first class river systems
throughout Japan
Riverine estuary environments were classified using
the river flow rate, riverbed gradient, tidal range, andwave height, as the physical environmental indiceswhich determine riverine estuary environments. For
the concept guiding the selection of indices, wereferred to a past report 1). Riverine estuaries wereclassified by performing principal component analysisof the above indices, obtaining the principal
components and principal component scores, thenperforming cluster analysis of principal componentscores for principal components with an eigenvalue of
1 or more. Figure 1 shows the distribution of riverine estuaries
classified into five classes based on indices values atnormal time. It established five classifications: a groupwhere the tidal range is a little large distributed widelyon the Pacific Ocean side (Tide Class I), Flow RateClass I where the river flow rate is a little highdistributed widely throughout Japan, Tide Class II
where the tidal range is extremely large and which is
distributed on part of the Ariake and Seto Inland Seas,
Gradient Class where the riverbed gradient is steep
distributed on the Hokuriku Tokai coast, and Flow RateClass II where the gradient is mild and flow rate is highlocated mainly at large rivers on the Japan Sea side.ClusterNameྡ⛠ࢡࣛࢫࢱ࣮
1₻ộϨᆺ
TideClass I
Flow Rateὶ㔞Ϩᆺ 2Class ITideClass II₻ộϩᆺ 3Gradient 4໙㓄ᆺ
Sea of JapanClassFlow Rate
 5ὶ㔞ϩᆺClass IIPacificOcean

Figure 1. National Distribution of Classification Basedon Indices at Normal Time3. SummaryThis classification clearly demonstrated for the firsttime relationships showing that in tidal type riverineestuaries strongly impacted by the sea, salt-water andbrackish water fish species are numerous, and that inflow rate type riverine estuaries strongly impacted byrivers, fresh water fish species are numerous 1). In thefuture, we will do further study of environmental
classifications and their properties to contribute to theconservation of riverine estuary environments.
[Reference]

1) Kishida, Amano, Onuma, Endo: Riverine estuary
classification for the sake of environmental
conservation, Journal of Hydraulic Engineering, JSCE,
Vol. 55, 2011. (in Japanese with English abstract)

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